Bumps [acorn](https://github.com/acornjs/acorn) from 6.1.1 to 6.4.1. - [Release notes](https://github.com/acornjs/acorn/releases) - [Commits](https://github.com/acornjs/acorn/compare/6.1.1...6.4.1) Signed-off-by: dependabot[bot] <support@github.com>